Generally, exhaust gas that is exhausted through an exhaust manifold of an engine is induced to pass through a catalytic converter that is mounted in the middle of an exhaust pipe to be purified, and noise thereof is reduced while passing through a muffler before the exhaust gas is discharged to outside through a tail pipe.
The catalytic converter processes pollution materials that are included in the exhaust gas. Further, a particulate filter is mounted on the exhaust pipe to trap a particulate material (PM) that is included in the exhaust gas.
A selective catalytic reduction device is a type of catalytic converter. Reducing agents such as carbon monoxide, total hydrocarbon (THC), and so on react well with nitrogen oxide rather than oxygen in the selective catalyst reduction apparatus (SCR).
In a case of an internal combustion engine to which the selective catalyst reduction apparatus is installed, in a normal driving mode of a diesel engine with oxygen, a nitrogen oxide exhausted from the engine and ammonia generated by a urea directly injected and supplied to the exhaust pipe are selectively reacted such that the nitrogen oxide is converted into a harmless nitrogen (N2) and then is removed.
However, an exhaust gas temperature must be 180 degrees (° C.) or more to be converted into ammonia in a urea solution. Accordingly, the exhaust gas temperature is low during an initial cold start and an urban driving, urea can be not injected and purification of the nitrogen oxide is impossible.
To ensure the activation of the selective catalytic reduction in a low temperature, a demand amount of the urea is high, in the case less than 250 degrees, since ammonia stored in the selective catalytic reduction is slipped in atmosphere after being attached or detached as the exhaust gas temperature increases, a urea injection amount is restricted such that performance of the selective catalytic reduction device is deteriorated.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.